DESCRIPTION: P450 1B1, which preferentially forms carcinogenic metabolites from PAHs is selectively expressed in stromal fibroblasts. CYP1B1 is induced after binding or PAHs and TCDD to the AhR, but this response appears to very from cell to cell. The proposed research will elucidate mechanisms of regulation of CYP1B1 gene transcription and if the AhR is involved in this regulation. Key cis-regulatory elements will be identified with reporter gene constructs. Cis-elements regulating constitutive expression and TCDD/PAH activation of CYP1B1 will be deduced in the 1B1 upstream region. Associated in vivo changes in protein binding to cis-elements will be examined by PCR-enhanced footprinting. Protein complexes formed with key regulatory elements will be examined by gel shift mobility assays. The role of AhRin the regulation of 1B1 will be elucidated. Anomalies in the induction of 1B1 by PAH will be evaluated in terms of it localized intracellular depletion via metabolism at 1B1. In vivo expression will be analyzed in mouse tissue, where cell specificity of expression will be addressed. The role of the AhR in the expression of 1B1 will be dissected by use of AhR-deficient mice. The physiological function of 1B1 will be assessed by analysis of the effect of disruption of the 1B1 gene by homologous recombination in transgenic mice.